October 17, 1994
12:00 AM (EDT)

News Release Number: STScI-1994-41

Hubble Rules Out a Leading Explanation for Dark Matter

October 17, 1994: Astronomers have ruled out the possibility that red dwarf stars constitute the invisible matter, called dark matter, believed to account for more than 90 percent of the universe's mass.

Until now, the dim, small stars were considered ideal candidates for dark matter. Whatever dark matter is, its gravitational pull ultimately will determine whether the universe will expand forever or will someday collapse. Picking a region in our Milky Way Galaxy, astronomers predicted that Hubble should have spied 38 red dwarf stars if this class of objects harbored most of the dark matter. The diamond-shaped symbols in the left-hand image illustrate what scientists expected to see. Instead, they saw no stars.